基于DEM-FEM耦合方法的海上风机结构冰激振动分析

冰载荷是海上风机在寒区安全运行的重要影响因素之一,由其引发的冰激振动给风机结构带来了严重的危害. 本文通过离散元(discrete element method, DEM)-有限元(finiteelement method, FEM)耦合方法建立了寒区单桩式风机结构的 冰激振动模型.采用具有粘结-破碎性能的球体离散单元描述平整海冰损伤破坏行为,采用梁单元和三角形平板壳单元构造带有抗冰锥体的单桩式风机有限元模型.采用DEM-FEM耦合方法模拟不同冰速、冰厚条件下单桩式风机与平整冰相互作用过程,并且与IEC规范和ISO标准经验公式对比验证该耦合模型计算冰载荷的准确性.对比风机塔筒顶端和基础顶端的位移和加速度响 应时程,定性地给出风机结构不同部位振动响应行为差异性.风机不同部位动力特性差异原因为风机结构独特结构特点:下部为大刚度桩基和上部为高柔度塔筒,使其动力特征表现为主从式结构特性. “主-从式结构”特征使得结构在复杂的冰载荷作用下,风机塔筒(子结构)和桩基(主结构)表现为不同的响应行为,风机不同部位振动周期和加速度谱两者出现差异. 本文研究成果为海上风机抗冰设计和疲劳分析提供了有益参考. 

ANALYSIS OF ICE-INDUCTED STRUCTURE VIBRATION OF OFFSHORE WIND TURBINES BASED ON DEM-FEM COUPLED METHOD

The ice load is one of the most important factors that cannot be ignored for offshore wind turbines (OWTs) in cold regions. The ice-induced vibrations (IIVs) can bring serious fatigue and damage to the OWTs structure. In this paper, a coupling method of the discrete element method (DEM) and the finite element method (FEM) is adopted to establish the IIVs model of monopile-type OWTs. The breakage and failure process of level ice are simulated with the spherical DEM with bonding-breaking effect, and the finite element model of monopile-type OWTs is constructed by the beam element and triangular plate shell element. The DEM-FEM coupled method is adopted to simulate the interaction progress between monopile-type OWTs and level ice under different ice velocity and ice thickness conditions. The accuracy of ice load calculated by the DEM-FEM coupled method is verified by comparing with the empirical formula of IEC (International Electrotechnical Commission) and ISO (the International Organization for Standardization). By comparing the displacements and the acceleration of the top of the wind turbine tower and the top of the foundation, the dynamic response characteristic of the OWTs is qualitatively analyzed. The reason for the difference of dynamic characteristics in different parts of OWTs is structural model characteristic of OWTs:the lower part is a large stiffness pile foundation and the upper part is a high flexibility tower, which makes its dynamic characteristic show the characteristics of the main and subordinate structure. The characteristics of “Main-Subordinate structure” make the tower (subordinate) and pile foundation (main) show different response behaviors under complex ice load, and the vibration period and acceleration power spectrum density (PSD) of different parts of OWTs are different. This study can provide a useful reference for the OWTs anti-ice design and the fatigue analysis of OWTs in cold regions.